HTTP Status Codes

A plain-English reference to the status codes you'll actually meet while building and debugging web services.

1xx — Informational

100	Continue — Request headers received; client should send the body.
101	Switching Protocols — Server agrees to switch protocols, e.g. to WebSocket.

2xx — Success

200	OK — The request succeeded.
201	Created — A new resource was created, typically after POST.
204	No Content — Success with no response body, common for DELETE.
206	Partial Content — A byte-range response, used for downloads and video streaming.

3xx — Redirection

301	Moved Permanently — Resource has a new permanent URL; browsers and search engines update.
302	Found — Temporary redirect; the original URL should keep being used.
304	Not Modified — Cached copy is still valid; no body returned.
307	Temporary Redirect — Like 302 but the request method must not change.
308	Permanent Redirect — Like 301 but the request method must not change.

4xx — Client errors

400	Bad Request — Malformed syntax or invalid parameters.
401	Unauthorized — Authentication required or failed.
403	Forbidden — Authenticated but not allowed to access this resource.
404	Not Found — The resource does not exist at this URL.
405	Method Not Allowed — The HTTP method is not supported for this resource.
408	Request Timeout — The client took too long to send the request.
409	Conflict — The request conflicts with current state, e.g. duplicate entry.
413	Payload Too Large — Request body exceeds the server limit.
415	Unsupported Media Type — The Content-Type is not accepted.
422	Unprocessable Entity — Well-formed request with semantic errors; common in REST APIs.
429	Too Many Requests — Rate limit exceeded; check the Retry-After header.

5xx — Server errors

500	Internal Server Error — Generic unhandled server failure.
501	Not Implemented — The server does not support the request method.
502	Bad Gateway — An upstream server returned an invalid response, common behind proxies.
503	Service Unavailable — Server temporarily overloaded or down for maintenance.
504	Gateway Timeout — An upstream server did not respond in time.

Reading the first digit

1xx informational, 2xx success, 3xx redirection, 4xx the client did something wrong, 5xx the server did. When debugging: a 4xx means fix the request; a 5xx means look at server logs.

The ones worth memorizing

200, 201, 301, 302, 304, 400, 401, 403, 404, 429, 500, 502, 503 cover the overwhelming majority of everything you'll ever see in logs and API responses.